1. Field of Invention
This invention relates to a nuclear magnetic resonance (NMR) probe and magnetic resonance imaging (MRI) utilizing radio frequency (RF) signals; and more particularly, to such a probe having an inner detection resonator combined with an outer resonator consisting of a spiral irradiation coil to thereby minimize the mutual inductance between the two resonators. Sensitivity is improved by means of an inner resonator consisting of a birdcage coil or dual saddle coils operated in the quadrature mode. Further sensitivity enhancement is obtained by cooling the resonators, or by fabricating one or more of the resonators from a superconductive material and operating in the superconducting temperature region.
2. Related Art
The following disclosures show related art:    1. U.S. Pat. No. 6,100,694, Aug. 8, 2000, W. H. Wong.    2. U.S. Pat. No. 6,420,871, Jul. 16, 2002, W. H. Wong, S. Uno, and W. Anderson.    3. U.S. Pat. No. 4,694,255, Sep. 15, 1987, C. E. Hayes    4. “Quadrature Detection Coils. A further √2 Improvement in Sensitivity”, C. N. Chen, D. I. Hoult, V. J. Sank, J. Mgn. Reson. 54, 324-327 (1983).    5. “A Hybrid Birdcage Resonator for Sodium Observation at 4.7 T”, P. Pimmel and A. Briguet, Mgn. Reson. Med. 24, 158 (1992).    6. “A New Miniaturizable Birdcage Resonator design with Improved Electric Field Characteristics”, S. Su, and JJ. K. Sanders, J. Magn. Reson. Ser. B, 110, 210-212 (1996).    7. “Optimized Small Bore, High Pass Resonator Designs” S. Crozier, K. Luescher, L. K. Forbes, D. M. Doddrell, J. Magn. Reson. Ser. B. 109, 1-11 (1995).    8. “Design and Performance of a Double Tuned Birdcage Coil”, A. Rath, J. Magn. Reson. 86, 488-495 (1990).    9. “5 mm Birdcage Coils for Micro-imaging Applications”, Wong, J. Finnigan, and S. Sukumar, Poster 171, 41st ENC, April 2000.
High resolution NMR probes typically have an inner saddle coil for irradiation and detection of a first nuclear species, and a second larger saddle coil coaxial with the inner saddle coil for irradiation of one or more other nuclear species. The two saddle coils are oriented 900 with respect to each other to minimize coupling between the two coils.
Normally, only one outer coil is used as additional saddle coils would strongly couple together or couple to the inner saddle coil, thus resulting in a loss of sensitivity and an increase of complexity in tuning the individual coils. More irradiation frequencies are achieved by double or triple tuning the outer saddle coil. The process of double tuning decreases the efficiency of the coils, thereby requiring more drive power to cause the desired nuclear resonance transitions.
Accordingly, it can be appreciated that the related prior art does not provide a multifrequency tuned quadrature probe design for an RF probe which has high resolution and with capacity for multifrequency decoupling. Moreover, the art is lacking such a probe, which has excellent sensitivity and efficient RF power usage and simplicity in structure.